Dental plaque biofilms are polymicrobial communities found on oral surfaces embedded in a matrix of host salivary components and microbial extracellular products. These biofilms provide an infection source for diseases of the oral hard and soft tissues. Communication reactions between the micro-organisms modulate the structure, composition and pathogenic potential of the biofilms. The oral streptococci are especially important in this respect because they are primary colonizers of oral cavity surfaces. Their deposition provides an attachment substrate for colonization by potentially pathogenic organisms such as the fungus Candida albicans, which is the cause of most yeast infections in humans. Co-adhesion between oral streptococci and C. albicans is proposed to facilitate oral carriage and persistence of C. albicans, leading to disease conditions such as denture-induced stomatitis. Studies have demonstrated that inter-microbial binding of Streptococcus gordonii and C. albicans involves complementary and co-operative adhesin- receptor molecules. Streptococcal cell surface-associated antigen I/II family adhesins, designated SspA and SspB, target yeast cell surface receptors, resulting in close engagement of other surface molecules on the partner cell types. These adhesion processes drive the development and accumulation of mixed species biofilms that are morphologically, physiologically and pathogenically unique. The objectives of this application are to: identify the C. albicans receptor for the SspB protein of S. gordonii; define the molecular basis of yeast receptor recognition by antigen l/ll family proteins; investigate the effects of substratum composition, environmental factors and the role of Streptococcal adhesin expression on the development of S. gordonii-C. albicans mixed biofilms; determine patterns of differential gene expression in S. gordonii and C. albicans in biofilms and induced by cell-cell contact. These experiments will provide detailed molecular information on the major components mediating interactions of S. gordonii and C. albicans and better understanding of the signals and pathways by which co-adhesion leads to biofilm maturation. Such information will assist in the development of more effective biologically based strategies for control of polymicrobial biofilms, and for therapeutic prevention of C. albicans overgrowth. Candida yeast infections are a serious threat to public health. This research devises new methods for controlling or preventing growth of Candida in the mouth. [unreadable] [unreadable] [unreadable]